The proposed project is intended to advance and develop a general theory of lexical creativity dealing with the structure, function, acceptability and relative utility of lexical and grammatical devices, old and new. The proposed experiments will test and refine the theory, using sophisticated reaction time techniques, (a) to determine whether and when a language can be said to need a new word to express a concept, (b) to compare the relative acceptability of sets of proposed new words and the factors governing the learning, hearing, reading, understanding, production and actual use of new words, (c) to determine the psychological effects of losing a frequently used lexical item, (d) to compare the advantages and disadvantages of a lexical item vs. a phrase or other grammar-based device for expressing the same concept, (e) to compare the imageability of lexical vs. grammatical expressions of the same concept, (f) to determine the patterns of use, lexical structure and functions of third person pronouns, (g) to explore the dimensions of lexical acceptability and resistance to lexical innovation. The special significance of this project is its originality, scope, and potential for practical application.